1. Field of the Invention
The present invention relates to a conductive polymer composition and a method of producing the same. The present invention further relates to a solid electrolytic capacitor provided with the abovementioned conductive polymer composition.
2. Description of the Related Art
A conductive polymer material is used for electrodes of a capacitor, a dye-sensitized solar cell, and an electroluminescent display, etc. As such conductive polymer material, highly molecularized polymer materials, such as pyrrole, thiophene, 3,4-ethylenedioxythiophene, and aniline, are well known. The conductive polymer material disclosed in Japanese Patent Nos. 2636968 and 4077675, which is formed using a conductive polymer suspension with polyanions as a dopant, attracts attentions in the field of electronic materials or the like as such conductive polymer material exhibits high conductivity.
Japanese Patent No. 2636968 describes polythiophene dispersions, their production, and the use of the salts for the antistatic treatment of plastic moldings. Further, Japanese Patent No. 4077675 discloses an aqueous dispersion of composite of poly(3,4-dialkoxythiophene) with polyanions and a method for producing the same, a coating composition including the aqueous dispersion, and a coating substrate including a transparent conductive film having the composition coated thereon. Both of the disclosures by Japanese Patent Nos. 2636968 and 4077675 are characterized by polythiophene made of the structural units of 3,4-dialkoxythiophene, polythiophene dispersions containing polyanions of polystyrene sulfonic acid origin, a method of producing the same, and the use of the salts for the antistatic treatment of plastic moldings.
Such conductive polymer composition, which is formed using a conductive polymer dispersion solution with a polyanion having multiple hydrophilic functional groups, includes multiple hydrophilic functional groups originated from polyanions not doped to conductive polymer in a conductive polymer composition. An undoped hydrophilic functional group has extremely high hydrophilic property as compared with a doped hydrophilic functional group.
Thus, there are faults that the conductive polymer composition having multiple undoped hydrophilic functional groups is generally low water resistance and is remelted to a polar solvent such as water.
Moreover, a solid electrolytic capacitor using this conductive polymer composition for a cathode layer has a disadvantage that reliability and characteristics deteriorates especially under high humidity atmosphere.
In order to solve the problems of the conductive polymer composition with multiple hydrophilic functional groups, Japanese Patent No. 3722839 and Japanese Unexamined Patent Application Publication No. 2001-270999 disclose a method to add a resin or the like that reacts with hydrophilic functional groups. Japanese Patent No. 3722839 describes a soluble conductive polymer having a sulfonic acid and/or a carboxylic acid self-doped functional group in a conductive polymer chain, a composition including a cross-linking compound having at least 2 or more functional groups which are capable of reacting with the self-doped functional group, a cross-linking electrical conductor formed by reacting the soluble conductive polymer and the cross-linking compound, and an antistatic treatment and a capacitor using the cross-linking electrical conductor. The disclosure of Japanese Patent No. 3722839 is characterized by containing a conductive polymer having a hydrophilic self-doped functional group in a molecule chain because of its soluble property and a cross-linking compound having 2 or more functional groups capable of reacting with the self-doped functional group. The functional group is selected from a hydroxyl group, a silanol group, a thiol group, an amino group, and an epoxy group.
Japanese Unexamined Patent Application Publication No. 2001-270999 describes a soluble conductive polymer having a sulfonic acid and/or a carboxylic self-doped functional group in a conductive polymer chain, and a composition including a silane coupling agent and/or colloidal silica having a functional group capable of reacting with the self-doped functional group. Japanese Unexamined Patent Application Publication No. 2001-270999 further describes a cross-linking electrical conductor formed by reacting the abovementioned soluble conductive polymer and the cross-linking compound. The disclosure of Japanese Unexamined Patent Application Publication No. 2001-270999 is characterized by containing a soluble conductive polymer having a hydrophilic self-doped functional group in a molecule chain because of its soluble property and a silane coupling agent and/or colloidal silica having one functional group capable of reacting with the self-doped functional group. The functional group is selected from a hydroxyl group, a thiol group, an amino group, and an epoxy group.
As compared to a conductive polymer having a hydrophilic self-doped functional group in a molecule chain, the conductive polymer composition formed using a conductive polymer dispersion solution with polyanions as a dopant has higher conductivity but lower water resistance as multiple undoped hydrophilic functional groups exist in the conductive polymer composition.